JPH0231600A - Electret capacitor microphone - Google Patents

Abstract

PURPOSE:To reduce the parts cost and assembling cost of the title microphone by using the top of a case as a fixed electrode and putting input leads of amplifier blocks with FETs fixed to printed circuit boards between a donut-like metallic ring fixing a diaphragm and the printed circuit boards and conducting the reeds. CONSTITUTION:The assembling work of this electret capacitor microphone is completed when a donut-like metallic ring 12 in which amplifier blocks, each of which is composed of a field effect transistor(FET) 9 and printed circuit board 10, are successively fitted beforehand is fitted in a cylindrical metallic case 11 and caulking 11c is performed to the printed circuit board 10. Since the top 11a can be used as a fixed electrode and no spacer is required for a gap, this microphone can be constituted with a less number of parts. Therefore, the assembling work can be simplified and cost can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electret condenser microphone that is simple in construction and inexpensive.

(Prior technology) Electret condenser microphone (hereinafter referred to as E
There are two types of CMs: a membrane (wheel) electret type in which an electret material is used for the vibrating membrane, and a pack electret type in which an electret material is fixed to the fixed electrode side by fusion or the like.

The following explanation deals with the former case. FIG. 7 shows a cross-sectional view of an example of a conventional ECM. In the figure, 1 is a cylindrical metal case, which has a sound hole 1b in its top surface 1a. 2
is a metal ring, the vibrating membrane 3 is fixed under tension on the end face thereof, and one side of the vibrating membrane 3 is coated with a metal vapor deposited film 3a. 4
is a gap spacer, which forms a capacitor 6 between the vibrating membrane 3 and the fixed electrode 5. Further, the brake hole 5a of the fixed electrode 5 is bored to ventilate the back air chamber 7. 8
is an insulator, houses a field effect transistor 9 (FET) for impedance conversion, and is used to fix the position of the fixed electrode and insulate it. 10 is a printed circuit board to which the output lead 9b of the FET 9 is fixed by soldering. Also F
The input lead 9a of the ET9 is electrically connected to the fixed electrode 5 by contacting or spot welding.

An exploded view for assembling the above-mentioned parts is shown in FIG. 8. This figure is an inverted version of FIG. 7, and the fixed electrode 5. Insulator 8. The FET 9 (which is inside an insulator and is not shown in the drawing) and the printed circuit board 10 are pre-processed to form an amplifier block, and a metal ring 2. Insert the gap spacer 4 and the pre-processed amplifier block (fixed electrode 5, etc.) one after another (
arrow) and swage the end of the metal case 1 (swiveled portion 1c).
) and has a fixed structure.

This utilizes the fact that the diaphragm 3 vibrates due to the sound pressure input through the sound hole 1b, and the capacitance of the capacitor 6 formed by the diaphragm and the fixed electrode 5 placed opposite to it changes. It is. Since the capacitor capacitance has a very high impedance at audio frequencies, when applying a DC electric field, the FET 9 is used as an impedance conversion element.

(Problem to be solved by the invention) As can be seen from the structure of the conventional ECM described above.

It has a fixed electrode 5 formed separately, and requires a gap spacer 4 for forming a capacitor 6 with the vibrating membrane 3. Since the number of parts is large and the structure is complex, it requires a lot of assembly man-hours and is not inexpensive. Also, since there are many internal parts, the back air chamber cannot be enlarged.

The present invention is intended to solve these drawbacks of the conventional structure, and aims to simplify the structure and reduce costs by minimizing the number of parts.

(Means for Solving Problem W) In order to achieve the above object, the present invention uses the top surface of a cylindrical metal case as a fixed electrode, and adhesively fixes a vibrating membrane on one side of which metal is vapor-deposited to one end surface of a donut-shaped metal ring. A capacitor is formed between the top surface and the vibrating membrane, a step is formed on the other end surface of the donut-shaped metal ring, and an input lead of a field effect transistor for impedance conversion is fixed to a printed circuit board. , it is characterized in that it is positioned at the stepped portion and is sandwiched between and press-contacted with the printed circuit board.

(Function) The present invention has the following effects due to the above configuration. In other words, since the FET is fixed to the printed circuit board as one amplifier block, there is no need to integrate the fixed electrodes, insulators, etc. that form the capacitor as in the past.
In addition, since conduction with the input lead of the FET can be established easily, the structure is simple, assembly is easy, and costs can be reduced.

(Embodiment) FIG. 1 is a sectional view showing an embodiment of the present invention, and the same parts as in FIG. 7 are indicated by the same numbers. In the same figure,
Reference numeral 11 denotes a cylindrical metal case, in which a plurality of sound holes 11b are bored in the top surface 11a, and a recessed portion lid is formed in the top surface 11a. This recess is, for example, on the order of several tens of inches. 12
is a donut-shaped metal ring.

A vibrating membrane 3 is tensioned and adhesively fixed to one end surface, and a stepped portion 12a is provided at the other end and fixed to a printed circuit board 10.

The input lead 9a of the FET 9 is positioned on this stepped portion 12a, and is sandwiched and pressure-contacted with the printed circuit board 10, and fixed (crimped portion 11c) by means such as caulking.

FIG. 2 shows each side of the stepped portion 12g, and FIG. 2(a) is an external view of the donut-shaped metal ring 12 shown in FIG. , a stepped portion 12a consisting of a convex portion 12a-2 is formed.

The stepped portion 12a may be divided by a separate insulator 12-1b and fixed to the end surface of the metal ring 12, as shown in FIG. 1(b). The recess 12a-1 shown in FIG. 3A and the opening 12-2b shown in FIG. 2B serve as outlets for the output leads 9b.

Next, the formation of the capacitor 6 will be described. The structure is opposite to the conventional one (FIG. 7) (the vibrating membrane 3 is arranged at a constant interval below the top surface 11a which serves as a fixed electrode).
Therefore, since the sound hole 11b may impede the shielding effect against induced noise (hum, etc.),
For example, when the diameter of the capacitor is about 10 m, it has been confirmed from experimental results that a shielding effect can be obtained by making the sound holes 11b have about 6 or less small holes with a diameter of about 0.5 square meters.

In addition, since the structure does not include the insulator that houses the FET 9 as in the conventional structure, there is a risk of a short circuit between the cylindrical metal case 11 and the donut-shaped metal ring 12. ) to (d) are used to prevent this.

FIG. 3(a) shows a case where the corner where the top surface 11a and the side wall lie of the cylindrical metal case 11 are joined is not formed at a right angle, but is shaved to create a so-called C-plane structure. b) and (c) show that when the diaphragm 3 is cut larger than the metal ring 12 and used for insulation, (d) of the same figure shows that the diaphragm 3 is cut larger than the metal ring 12 to be used as an insulator. This is a case where the position of the ring 12 is fixed.

FIG. 4 shows an exploded view of parts showing the assembly of this embodiment.
It is a state diagram where the figure is turned upside down. FET in advance as shown
The assembly is easily completed by fitting the amplifier block consisting only of the amplifier block 9 and the printed circuit board 10 into the donut-shaped metal ring 12 in the direction of the arrow, and then fitting it into the cylindrical metal case 11. The substrate 10 is caulked (llc).

As described above, in this embodiment, unlike the conventional fixed electrode 5, the fixed electrode 5 is not provided, and the top surface 11a is also used, and the gap spacer 4 is not required, so the number of internal parts is small, and the back air chamber is You can make it bigger. Furthermore, it can be easily assembled as described above, and the cost can be reduced.

Next, regarding the operation of this embodiment, the capacitor 6 is formed between the recess lid of the top surface 11a and the vibrating membrane 3.

Therefore, the concave portion becomes a gap, and the diaphragm 3 plays the role of insulation, so the diaphragm 3 vibrates due to the sound pressure input from the sound hole 11b, causing a change in the capacitance of the capacitor 6. and is input to FET9.

5 and 6 are cross-sectional views showing another embodiment of the present invention. In FIG. 5, a convex portion 21d is formed in the center of the top surface 21a of a cylindrical metal case 21, and a vibrating membrane 3
In this case, the capacitor 6 is formed between the sound hole 21b and the sound input from the sound hole 21b by providing a plurality of convex portions 21d at predetermined intervals along the outer periphery of the center portion of the top surface 21a instead of providing it at the center. The sound pressure allows the capacitor 6 to operate efficiently.

Fig. 6 shows a case where a metal ring 2 is used in addition to the donut-shaped metal ring 12, and the vibrating membrane 3 is adhesively fixed to the metal ring 2. It is a comb that is easily transmitted from to 12.

(Effects of the Invention) As explained above, the present invention has the top surface of the case as a fixed electrode, and the input lead of an amplifier block in which an EFT is fixed to a printed circuit board, and a donut-shaped metal ring to which a vibrating membrane is fixed and a printed circuit board. Since conduction is provided by sandwiching the amplifier block between them, the number of components can be reduced, and the amplifier block can be simplified, which has the advantage of reducing component costs and assembly costs. Furthermore, since there are fewer internal components, the back air chamber can be enlarged, making it possible to achieve higher sensitivity.

Although not described in this embodiment, in the case of a configuration in which the output lead 9b of the FET is extended several meters perpendicularly to the printed circuit board without bending or cutting (ECM with legs), four internal components are Since no insulator is used, it is advantageous in terms of heat resistance, and since the electret surface of the vibrating membrane is not on the inner surface side, it also has the advantage that it is less affected by full flux even if it enters the inside.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention, FIG. 2 is an external view showing an example of the structure of the stepped portion of the metal ring 12, and FIG. FIG. 4 is an exploded view of parts for explaining the assembly of this embodiment, FIGS. 5 and 6 are cross-sectional views of other embodiments of the present invention, and FIG. 7 is an example of a conventional electret condenser microphone. The sectional view and FIG. 8 are exploded views showing the assembly. ...Vibration membrane, 3a...Metal deposited film, ...Capacitor, 7...Back air chamber. ... Field effect transistor (FET), ... Input lead, 9b... Output lead, ... Printed circuit board, 11.21... Cylindrical metal case, 11a. 1a Top surface. 11b. 1b sound hole, ie caulking part. id recess, ie side wall, 2a step, 1d protrusion.

Claims (1)

[Claims] The top surface of the cylindrical metal case is used as a fixed electrode, and a vibrating membrane having metal vapor deposited on one side is adhesively fixed to one end surface of a donut-shaped metal ring to form a capacitor between the top surface and the vibrating membrane. A stepped portion is formed on the other end surface of the shaped metal ring, and the input lead of a field effect transistor for impedance conversion fixed to the printed circuit board is positioned on the stepped portion and is sandwiched between and pressed against the printed circuit board. An electret condenser microphone that is characterized by: